Process of manufacturing expanded rubber



May 16, 1939.

F.'W.- PEEL PROCESS OF MANUFACTURING EXPANDED RUBBER Filed Aug. 22, 1936RUBBER SULPHUR FILLERS LOW TEMP ERATURE ACCELERATOR HIGH TEMPERATUREACCELERATOR MIXED ON MILL HEATING CHAMBER 180 TO 200 F.

LOW TEMPERATURE ACCELERATOR ACTUATED CAUSING PARTIAL VULCANIZATIONGASSING CHAMBER RUBBER DOUGH GASSED WHILE HOT COOLED AFTER GASSINGVULCANIZATION AND EXPANSlON IN MOULDs HIGH TEMPERATURE ACCELERATORACTUATED CAUSING COMPLETE VULCANIZATION INVENTOR.

ATTORNEY.

Patented May 16, 1939 PROCESS OF MANUFACTURING EXPANDED RUBBER FrederickWilliam Peel, London, England, as-

signor to Rubatex Products, Inc., New York, N. Y., a corporation ofDelaware Application August 22, 1938, Serial No. 97,418

9 Claims. (CI. 18-53) This invention relates to novel methods ofmanufacturing gas-expanded rubber.

The manufacture of gas-expanded rubber comprises subjecting a suitablerubber mixture to an inert gas at a very high pressure and entrappingthe gas within the rubber as small individual gas cells. Good qualitygas-expanded rubber must have a homogeneous structure, the individualgas cellular structure being of uniform size and even- 10 1y distributedthroughout the rubber mass. The gas expanded rubber product may be softor hard according to the composition used. The material may be moldedinto any shape or form; Gas expanded rubber is completely water-proof,is buoyant due to its light weight, is a good thermal insulator andpossesses marked acoustic absorption qualities.

Gas-expanded rubber, despite its inany valuable commercial qualities,has not gone into extensive industrial use. It could not heretofore beplaced on a competitive market with plain rubber, cork, Celotex and thelike. The primary object of this invention is to provide a novel processfor reducing the cost of the manufacture of gas-expanded rubberproducts.

The process for manufacturing gas-expanded rubber heretofore widelyaccepted as the most practical method for commercial production is theso-called two stage process. Such a process is the basis of the UnitedStates Patent No. 1,905,269, dated April 25, 1933, to Benton, and theco-pending application Serial No. 717,550 filed March 2'7, 1934, ofwhich ,I am a co-inventor. In the two-stage process, the rubber dough isgassed in an autoclave at a pressure of the order of 3000 pounds persquare inch and simultaneously heated to efiect a partial vulcanizationof the rubber to retain the adsorbed gas cells on removal from theautoclave, and subsequently finally cured and expanded in suitable moldsor containers.

An autoclave is .a steam-jacketed gassing chamber. The chamber is heatedby steam at a pressure of about eight pounds per square inch to raiseits walls to a temperature of 113 C. Precautions must be taken touniformly heat the rubber and not to overcure any portion of it. It isdiflicult to avoid possible undercuring of the internal portions of thedough charge if the outer portions are not to be over-heated. Inpractise the gassing chambers are therefore not charged beyond one-thirdof their full volume capacity and the charge is centrally located, so asnot to be too near the chamber walls.

The factors which rendered the prior processes commercially expensivewere that the gassing chamber was operated at one-third its nominalcapacity and that the gassing period was relatively long, requiringabout 1 to 2 hours for soft, and about '7 to 9 hours for hardgas-expanded rubber. Since the autoclaves together with the auxiliaryapparatus are highly expensive units, a large investment was necessaryfor each unit. The large initial expense together with the highmaintenance cost for the 3000 pound per square inch compressor, valvesand fittings, coupled with the low operating production efiiciency,raised the unit cost of the gas-expanded rubber product.

In accordance with my invention, I contemplate pre-heating the rubberdough to render it plastic before insertion in the gassing chamber. Thedough is homogeneously pre-cured in a room heated to a temperature ofabout F. to 200 F. The pre-cured dough is then placed into the gassingchamber and'subjected to an inert gas at a pressure of the order of 3000pounds per square inch for thorough gassing.

I have found that the gassing period is reduced to at least one-thirdthe time heretofore required when simultaneous heating of the charge wascarried out. A further important commercial advantage of pro-curing thedough resides in that the full capacity of the gassing chamber isutilized by a charge substantially filling the gassing chamber. Sincethe autoclave is not heated for partially curing the dough, no danger ofoverheating any portion of the charge is encountered and the wholechamber is available for gassing pre-cured dough. The final stage of mynovel process is similar to the second stage of the two-stage processes,namely, final vulcanization and expansion in a suitable mold.

I have also discovered that by utilizing two accelerators in the rubberdough, independently effective at the two heating stages, the efficiencyof my process is materially increased. By using an accelerator such asVulcaid P. (piperidine pentamethylene) effective at the pre-curingtemperature, the dough is efliciently rendered plastic and the adsorbedinert gas is effectively retained within the dough between the gassingand final curing stages. Diphenylguanidine, as the second accelerator,is effective during the final vulcanization temperature.

Accordingly, in accordance with my present invention, the utilization ofthe autoclave is increased at least nine or ten times over that of priorsystems, when calculated on a charge-hourly basis.

It is accordingly an object of my present invention to provide a novelthree-stage method for-manufacturing gas-expanded rubber.

/ It is another object of my invention to increase the productionutilization of the autoclave and s auxiliary equipment in themanufacture of gasexpanded rubber.

It is still another object of my invention to reduce the time requiredfor gassing a rubber charge in the manufacture of gas-expanded rubber. d

m It is a further object of my invention to increase the chargingcapacity of the gassing chamber in the manufacture of gas-expandedrubber.

It is another object of my invention toprovide a novel process formanufacturing gas-expanded rubber of very highquality at a competitiveprice.

It is still a further object of my invention to provide a novel processfor manufacturing gasexpanded rubber using two distinct acceleratorsindependently effective at the pre-curing and iinally curing stages.

These and other objects of my invention will be described inthefollowing detailed description of the production of a preferred softand hard gas-expanded rubber product.

For articles of soft gas-expanded rubber, the exemplary compound orcomposition comprises the following;

' Pounds Ounces Pale crepe 33 0 Light cal. magnesium 15 Lithopone 6 0Mag. oxide HY 6 9 Paramn wax 15 5 Zinc oxide 2 1 Sulphur 1 A Vulcaid P.(Piperidinium pentamethylene dithiocarbamate) D. P. G 4 ,5

40 Agerite powder 6% Carbon black 1% For articles of hard gas-expandedrubber, the exemplary compounds or composition comprises The rubber andthe other ingredients are mixed on the mill in a manner well known inthe art to prepare the rubber dough. The dough is then placed insuitable containers or coiled spring steel sheeting.

In the first stage of my process, the dough is pre-cured in a room orchamber at a temperature of the order of 180 F. to 200 I". The doughwithin the containers or coils is placed in the heated chamber for apredetermined period dependent upon the bulk of the dough until auniform and steady state heating of the dough is eifected. The heatingperiod may range from a half hour to two hours. The dough during thisfirst stage becomes plastic and also causes the accelerator Vulcaid P.(piperidine pentametliylcue) to be fully active. A very large bulk ofdough within separate containers may accordingly be homogeneouslypre-cured at very little cost. The second stage of my novel processconsists in gassing the plastic and pre-cured dough with 1 a neutral gasat a high pressure. It is important arsaoaa that the pre-cured dough notbechilled or otherwise reduced in temperature between -the first andsecond stages. The walls of the autoclave are accordingly heated toapproximate the temperature of the dough to avoid chilling thereof. Thiscan be done in a short time, for example, by blowing steam into the openchamber before introducing the dough.

The doors of the gassing chamber are sealed after the pre-cured chargeis placed therein. It is to be understood that the charge may comprisesubstantially the whole volume of the gassing chamber since no heattransfer is required during the second stage. A neutral or inert gas,for example, nitrogen, is admitted to the chamber at a pressure of theorder of 3,000

pounds per square inch. The gas is readily adsorbed by the plasticdough. The soft rubber mixture will be sufliciently gassed in a periodof about one-half hour; the hard rubber mixture, for a period of fromtwo to four hours.

When the dough is completely gassed, it is desirable to cool the chambertogether with the dough as rapidly as possible to a temperature of aboutF. This may be effected by circulating cold water through a jacketprovidedwithin the cylinder. The gas pressure is reduced to atmosphericpressure and the containers or coils containing the gassed and partiallyvulcanized dough are removed from the gassing chamber. The rubber isreleased from the containers or coils and it expands a considerableamount due to the pressure of the confined individual gas cells, and isthen ready for the third and final stage of my novel process.

The first and second stages of my novel process produce a gas-expandedpre-cured dough which is similar to the first stage of the priortwo-stage processes. However, a uniformly high quality is assured by mynovel process due to the independent pre-curing and gassing withoutdanger of uneven heating or over-heating of the dough. The pre-curing iseffected in a heated, inexpensive room or chamber at atmosphericpressure and atmospheric gaseous content. The gassing plant is utilizedto a maximum capacity since the gassing is, carried on independent ofthe partial vulcanization so that 100% capacity charges are used. Therelatively small period of charging reduces the cost per unit weight ofproduct considerably, since the high cost of the plant is economicallyutilized. I have found that ten times the production of gas-expandedrubber products is possible with substantially the same investment ofgassing equipment as compared to prior processes, greatly reducing thecost of production of the products to place them on a competitive basisin the open market with materials of similar properties.

The third stage of my novel process is the final vulcanization andexpansion stage carried on in molds and is similar to the second stageof the prior two-stage processes. The gassed partially vulcanized doughis placed into large containers of suitable shape or again rolled intocoils or placed in suitable molds and is subjected to the action ofadequate vulcanizingheat for a period sufficient to complete thevulcanization and also further expand the dough to completely fill theconfining molds or containers in a manner well known to those skilled inthe art. The. second accelerator, namely, D. P. G. is rendered active atthe final vulcanization temperatures.

Although I have described specific rubber compounds and preferredoperating parameters to carry out my process, it will be evident thatmodifieations are feasible and the actual temperatures, gas pressuresand periods of operation depend to some extent upon the composition andbulk of the rubber dough, and accordingly I do not intend to be limitedexcept as set forth in the following claims.

I claim:

1. In the process of manufacturing gas expanded rubber from rubberdough, the steps of incorporating a low temperature accelerator in thedough in such quantity as to produce partial vulcanization of the rubberupon heating, heating the dough to a temperature for rendering the lowtemperature accelerator fully active to partially vulcanize the dough,and subsequently gas impregnating the plastic dough with an inert gas.

2. In the process of manufacturing gas expanded rubber from rubberdough, the steps of incorporating a low temperature accelerator in thedough in such quantity as to produce partial vulcanization of the rubberupon heating, heating the dough at atmospheric pressure to a temperaturefor fully activating the low temperature accelerator and for renderingthe dough plastic and partially vulcanized, and subsequently gasimpregnating the plastic, partially vulcanized dough with a neutral gas.

3. In the process of manufacturing gas expanded rubber from rubberdough, the steps of incorporating a low temperature accelerator in thedough in such quantity as to produce partial vulcanization of the rubberupon heating, heating the dough at atmospheric pressure to a,temperature for fully activating the low temperature accelerator andfor rendering the dough plastic and partially vulcanized, andsubsequently gas impregnating the heated plastic partially vulcanizeddough with a neutral gas.

4. In the process of manufacturing gas expanded rubber from rubberdough, the steps of incorporating a low temperature accelerator in thedough in such quantity as to produce partial vulcanization of the rubberupon heating, heating the dough at atmospheric pressure to a temperaturefor fully activating the low temperature accelerator and for renderingthe dough plastic and partially vulcanized, and subsequently gasimpregnating the heated plastic, partially vulcanized dough with aneutral gas at a pressure of the order of 3000 pounds per square inch,and then rapidly cooling the gassed dough to a temperature of the orderof 60 F.

5. The method of manufacturing gas-expanded rubber which comprisesincorporating a low and a relatively higher temperature accelerator inthe rubber dough, said low temperature accelerator being present in suchquantity as to partially vulcanize the rubber upon heating, heating thedough for rendering the dough plastic, gas impregnating the heatedplastic dough with a neutral gas, removing the excess gas, and finallyvulcanizing the gassed dough.

6. The method of manufacturing gas-expanded rubber which comprisesincorporating a low and a relatively high temperature accelerator in therubber dough, said low temperature accelerator being present in suchquantity as to partially vulcanize the rubber upon heating, heating thedough at atmospheric pressure to a temperature for rendering the doughplastic, gas impregnating the plastic dough with a neutral gas withoutchilling the dough, removing the excess gas, and finally vulcanizing andexpanding the gassed dough in suitable molds.

7. The method of manufacturing gas-expanded rubber which comprisesincorporating a low and a relatively high temperature accelerator in therubber dough, said low temperature accelerator being present in suchquantity as to partially vulcanize the rubber upon heating, heating thedough at atmospheric pressure to a temperature for fully activating thelow temperature accelerator to effect a partial vulcanization of therubber dough to render the dough plastic, gas impregnating the plasticand partially vulcanized dough with a neutral gas without chilling thedough, subsequently rapidly cooling the gassed dough, removing theexcess gas, and finally vulcanizing and expanding the gassed dough insuitable molds at a temperature for rendering the higher temperatureaccelerator fully active.

8. The method of manufacturing gas-expanded rubber which comprisesincorporating a low and a relatively high temperature accelerator in therubber dough, said low temperature accelerator being present in suchquantity as to partially vulcanize the rubber upon heating, heating thedough at atmospheric pressure to a temperature for fully activating thelow temperature accelerator to effect a partial vulcanization of therubber dough and-to render the dough plastic, gas impregnating theplastic and partially vulcanized dough with a neutral gas at a pressureof the order of 3000 pounds without chilling the dough, and subsequentlyrapidly cooling the gassed dough to a temperature of the order of 60 F.and removing the excess gas, and finally vulcanizing and expanding thegassed dough in suitable mold at a temperature for rendering the highertemperature accelerator fully active.

9. The method of manufacturing gas-expanded rubber which comprisesincorporating a low and a relative high temperature accelerator in therubber dough, said low temperature accelerator being present in suchquantity as to partially vulcanize the rubber upon heating, heating thedough at atmospheric pressure to a temperature of the order of 180 F.for fully activating the low temperature accelerator to effect a partialvulcanization of the rubber dough and to render the dough plastic, gasimpregnating the plastic and partially vulcanized dough with nitrogengas at a pressure of the order of 3000 pounds without chilling thedough, and subsequently rapidly cooling the gassed dough to atemperature of the order of 60 F. and removing the excess gas, andfinally vulcanizing and expanding the gassed dough in suitable molds ata temperature for rendering the higher temperature accelerator fullyactive.

FREDERICK WILLIAM PEEL.

